Robert Kirkman

AMC, as expected, has renewed “The Walking Dead” for a fourth season, but the zombie drama will undergo another change at the top as showrunner Glen Mazzara announced that he will be leaving the series.

In a statement, AMC said, “the two parties have mutually decided to part ways.”

“Glen guided the series creatively for seasons 2 and 3,” the statement read. “AMC is grateful for his hard work. We are both proud of our shared success. Both parties acknowledge that there is a difference of opinion about where the show should go moving forward, and conclude that it is best to part ways.”

AMC described the decision as “amicable” and said that Mazzara will stay on through post-production on Season 3, which resumes Feb. 10.

“The Walking Dead” is AMC’s biggest hit — and one of the biggest hits on television, becoming the first basic cable show to lead the ratings in the highly coveted adults 18-49 demo. Even so, it has had its share of behind-the-scenes drama. Frank Darabont, who adapted the series from Robert Kirkman’s comic books, was abruptly forced out as showrunner midway through Season 2 for reasons that still haven’t been made clear.

In a separate statement, Mazzara said, “My time as showrunner on ‘The Walking Dead’ has been an amazing experience, but after I finish Season 3, it’s time to move on. I have told the stories I wanted to tell and connected with our fans on a level that I never imagined. It doesn’t get much better than that. Thank you to everyone who has been a part of this journey.”

Meanwhile, Kirkman issued his own extensive statement, saying, “I am in full support of both AMC and Glen Mazzara in the decision they have come to and believe the parties came to this decision in the best interest of the future of the show. I thank Glen for his hard work and appreciate his many contributions to ‘The Walking Dead’ and look forward to working with him as we complete post production on Season 3. I am also excited to begin work on another spectacular season of this show that I know means so much to so many people. This show has always been the result of a wide range of extremely talented men and women working tirelessly to produce their best work collectively. I believe the future is bright for ‘The Walking Dead.’ Thank you to the fans for your continued support.”

Despite those warm-and-fuzzy declarations, you have to wonder what exactly it was about Mazzara’s vision for the show that AMC objected to — and why the network would even want to mess with such amazing success. And “amicable”? Probably not.

Either way, fans have reason to be nervous. Under Mazzara’s direction, “The Walking Dead” became more tense and tough and gripping, even as it did up the gore quotient. The show landed on several end-of-the-year Top 10 lists issued by TV critics.